Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2001-02-20
2001-11-06
Wong, Peter S. (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S097000, C363S049000
Reexamination Certificate
active
06314003
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a switched-mode power supply having a rectifier configuration which supplies a rectified voltage at its output, a transformer with a primary winding and a secondary winding for connecting a load, a switching transistor for the clocked application of the rectified voltage to the primary winding, and a drive unit which controls the switching transistor.
In switched-mode power supplies the current flowing through the primary winding of the switched-mode power supply transformer is chopped by means of the switching transistor. The voltage pulses induced on the secondary side of the transformer are rectified and smoothed in order to supply a load with the D.C. voltage. The turn-on and turn-off phases of the switching transistor are controlled in dependence on the loading in such a way that the secondary voltage is regulated to be constant and as far as possible independent of load.
A power supply of the generic type is disclosed, for example, in my earlier, commonly assigned U.S. Pat. No. 5,420,776. The control unit there contains an integrated circuit designated TDA 4605 which, for the purpose of supplying the operating voltage, is connected via voltage dividers with a bridge rectifier. The latter rectifies the input A.C. voltage. The output of the control unit is connected to the control terminal of the switching transistor which is coupled with the primary winding. The withstand voltage of the control unit must thereby be chosen in dependence on the strength input A.C. voltage.
FIG. 3
of published PCT application Wo 97/50165 discloses a switched-mode power supply which has a rectifier configuration at the output of which a rectified voltage is available which, by means of a switching transistor, is applied to a primary winding belonging to a transformer and connected in series with the switching transistor. A drive circuit of the switching transistor is coupled to the secondary coil in that prior art switched-mode power supply, and is connected to a control terminal of the switching transistor by means of a transformer.
Published PCT application WO 98/03136 discloses a switched-mode power supply in which a D.C. voltage which is available is applied by means of a switching transistor to a primary winding belonging to a transformer and connected in series with the switching transformer. In order to drive the switching transistor, a pulse generator is provided, which is coupled to the control connection of the switching transistor by means of a transformer. In that case, the pulse generator is connected to a secondary coil of the transformer. In order to permit the switched-mode power supply to be started up, a start circuit configuration is provided on the primary side, which picks up energy from the D.C. voltage that is present on the primary side and which is connected to the control terminal of the switching transistor.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a switched mode power supply which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this general kind, and which is simplified in terms of its circuitry on the primary side.
With the above and other objects in view there is provided, in accordance with the invention, a switched-mode power supply, comprising:
a rectifier configuration having an output supplying a rectified voltage;
a transformer having a primary winding connected to the rectifier configuration and a secondary winding;
a switching transistor connected to the primary winding for a clocked application of the rectified voltage to the primary winding;
a drive unit for driving the switching transistor, the drive unit being coupled to the secondary winding and being D.C.-isolated from the switching transistor; and
a voltage source connected on a secondary side of the transformer for providing an operating voltage to the drive unit during a startup of the switched-mode power supply.
In accordance with an added feature of the invention, the drive unit is connected to the switching transistor via a further transformer.
In accordance with an additional feature of the invention, the drive unit is D.C.-connected to the secondary winding.
In accordance with a concomitant feature of the invention, the voltage source is a rechargeable battery or an electrolytic capacitor.
The invention has the advantage that commercial microprocessors can be used for driving the switching transistor. The drive unit does not have to be designed for the mains voltage; instead it can be designed for the lower voltage on the secondary side.
The driving function of the microprocessor can be undertaken by a processor which is already present in the device to be supplied with power by the switched-mode power supply, for example the deflection processor in television sets.
Driving the switching transistor by means of the microprocessor is very flexible and, by changing the software, can be adapted with a relatively low outlay and even for relatively small numbers. Driving is preferably carried out digitally, but can also be carried out analog.
Since the entire control outlay on the primary side is dispensed with, the latter substantially only contains the power transistor, the bridge rectifier, the mains filter and, possibly, a current pump for the sinusoidal current uptake.
Mains-voltage monitoring, short-circuit disconnection and further special functions, such as burst operation in standby, can likewise be implemented as software.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a switched-mode power supply, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
REFERENCES:
patent: 3935526 (1976-01-01), Kamata et al.
patent: 4694386 (1987-09-01), de Sartre
patent: 4695936 (1987-09-01), Whittle
patent: 4885673 (1989-12-01), Philippe
patent: 4912617 (1990-03-01), Hartmann et al.
Greenberg Laurence A.
Infineon - Technologies AG
Laxton Gary L.
Lerner Herbert L.
Stemer Werner H.
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